Is there a way to avoid admitting my engagement ring is not diamond, if i plan to upgrade to diamond soon?

I'm thinking of getting either cubic zirconia, moisannite, or white sapphire, but it will be the same carat as the diamond im replacing it with in about 2 years. it will be a relatively large rock, and we are young, so i think much of our family will obviously know its not a diamond, but i kind of want them to think it is. what should i do? i dont want to outright lie, but eventually it will be a diamond, and i dont want to seem trashy or cheap to my fiances family or our friends.